First of all, the Tupi language's background is rather complex. To sum it up briefly, it is a name for the group of similar languages that the Indians in Brazil use. The most common of these languages is Old Tupi, more commonly known as Nheengatu or the "fine language", spoken in the Rio Negro region.

Secondly, in the U.S.A and in the U.K., Jaci is either a nickname for Jacintha, Jacinda, or Jaclyn. Though I do have to admit the meaning for the Tupi word is pretty.

Alternatively, the name bestowed by two former hippies turned pillars of society, named Jack and Cieli, on their daughter (Ja + Ci = Jaci). Pronounced "jay-cee," not "jacky," though the accent is on the a.

I like this name because my little sister is named this and I've literally met no other Jaci's. I also like it because it rhymes with popular named like Macey and Lacey and Gracie and names that end with a prominent "e' sound.